The present invention relates to laminated windshields and particularly to laminated antenna windshields of the type depicted in U.S. Pat. Nos. 3,543,272 and 3,638,225 to Rodger V. Zawodniak. Such laminated windshields comprise a pair of sheets of relatively rigid material and a plastic interlayer in which is embedded antenna wire. One of the sheets of rigid material has a notched portion along its marginal periphery where an exposed portion of the antenna wire is connected to an electroconductive element. The latter, in turn, is adapted to be coupled to a radio receiver so that the antenna wire embedded within the interlayer of the laminated windows serves as an antenna for the radio.
Typically, laminated automobile windshields are fabricated by bending a pair of glass sheets of matching outline except for a small notched portion along one longitudinal side edge of one of the glass sheets while the latter are aligned on a bending mold, sewing an elongated antenna wire into a sheet of plasticized polyvinyl butyral that serves as an interlayer, assembling the pair of shaped glass sheets with the interlayer sheet therebetween for lamination, prepressing the assembly to remove entrapped air and fluid and seal the glass sheets to the margin of the interlayer and finally laminating the prepressed assembly in an oil autoclave. Adequate sealing of the marginal edge of the assembly during prepressing is vital to provide a barrier to the inward flow of oil between the layers of the assembly during final lamination. Prior to the advent of the antenna windshield, in laminated windshields whose aligned glass sheets had aligned margins uninterrupted by an offset notched portion in one of the sheets, the marginal barrier of interlayer material bonded to the aligned glass margins could be made impervious to the flow of oil between adjacent layers of the assembly during final lamination in an oil autoclave by thickening the marginal portion of the interlayer while still hot from the prepressing step using the edge rolling technique of U.S. Pat. No. 2,999,779 to Morris. However, it is not possible to use edge rolling in the vicinity of the notched portion without danger to the antenna wire.
The notched portion of one of the sheets of rigid transparent material, such as glass sheets, occupies the lower central portion of an automobile windshield when installed in a vehicle. The other glass sheet and the interlayer sheet extend throughout the entire extent of the windshield substantially, thereby providing a notched portion wherein the portion of the antenna wire outside the interlayer sheet can be attached to a metal plate or tab, which, in turn, is connected to a lead wire which leads to a radio receiver or is adapted to be connected to a radio receiver.
During the fabrication of laminated antenna windshields for automobiles, the portion of the antenna wire to be connected to the metal plate or tab must leave the interior of the interlayer sheet. The notched portion of the notched glass sheet is made slightly larger than the tab to be inserted, sufficiently small to avoid too great a deviation in dimensions between the glass sheets, yet large enough to insure that the entire tab can be inserted in the notched portion in spaced relation to the perimeter of the windshield to avoid grounding the tab against the frame of an automobile when the windshield is installed. Since the tab is made as small as possible in order to avoid too much interruption to the transparency of the laminated window, an operator is likely to imbed the antenna wire in the interlayer sheet in such a manner that a portion of the antenna wire extends from the interior of the interlayer sheet a distance from the edge of the sheet greater than the transverse distance of the notched portion of the rigid transparent sheet in which the connection is made to the metal tab. In such a case, the thickness of the antenna wire portion outside the interlayer and misaligned with the notched portion causes a separation between the notched glass sheet and the interlayer sheet in the vicinity of the notched portion.
Even though the assembly of two glass sheets and interlayer sheet is preliminarily pressed or tacked together by either heating and evacuation throughout the margin by the so-called glass bag technique disclosed in U.S. Pat. No. 2,948,645 to Laurence A. Keim, or the glass-plastic assembly is prepressed by roll prepressing apparatus such as that disclosed in U.S. Pat. No. 3,351,001 to Anthony A. Achkio, where the assembly to be prepressed is passed through an oven and heated to approximately 150.degree. F. (approximately 65.degree. C.) and roll pressed at that temperature followed by additional heating to approximately 190.degree. F. (about 88.degree. C), such preliminary pressing has not been able to seal completely the plastic interlayer sheet to the notched glass sheet in the vicinity of the antenna wire when the latter extends out of the interlayer material interior of the notched portion.
An attempt was made to fill this unsealed area by applying additional interlayer material across the interface between the glass and the plastic interlayer occupied by the exposed antenna wire adjacent the inner boundary of the notched portion. However, this proposed solution did not eliminate the problem. When the assembly with its antenna wire was laminated at elevated temperature and pressure in an oil autoclave, some oil penetrated along the wire and extended into the viewing area of the windshield to provide a reject in production.